The invention relates generally to a scanning micro-fluid device, and more specifically, to a scanning micro-fluid device for an exchange of species with a surface and an intermediate immersion liquid. The invention relates further to a method for an exchange of species with a surface and a related method.
Local processing of substrates is required in various applications including biology, chemistry, medicine, biotechnology, optics, microfabrication, electronics and materials science and engineering. Such processing involves locally altering a substrate for additive patterning or extraction of molecules by confining the contact of reagents to a limited area on the sample. These reagents may be delivered to the substrate by fluid motion or electro-kinetic transport. In particular, local processing and analysis of samples at the microscale is advantageous in biological applications, in which standard samples include tissue sections, adherent cells, and DNA or protein microarrays.
Electro-kinetic transport is beneficial for processing and analysis of biological samples at the micrometer and sub-micrometer scale due to the dominance of electro-kinetic phenomena at these scales and their compatibility with microfluidic devices. Furthermore, electro-kinetic phenomena are commonly used to manipulate analytes, as biological cells and most biomolecules are electrically charged, and are directly affected by an interaction with electric fields. For example, interactions with cell membrane leading to electroporation, focusing, separation and mixing of analytes.
Two common transport mechanisms occur when an electric field is applied which are electrophoresis and electro-osmosis. Electrophoresis refers to motion of ions in solution under the influence of an external electric field. The velocity of the ion migration is proportional to the applied electric field. The proportion coefficient is termed electrophoretic mobility and depends on the ion charge and the viscosity of the fluid. Electro-osmosis refers to bulk fluid motion, occurring when electric fields are applied across microfluidic channels or capillaries. This Velocity depends on the material the walls of the micro-channel are constructed of and the solution that comes in contact with the walls. This fluid motion is called electro-osmosis, or electroosmotic flow (EOF), and the proportion coefficient to the electric field is the electroosmotic mobility. EOF occurs as a result of electrical forces exerted on ions in the electric double layer (EDL) in the liquid adjacent to the wall.